Associated Topics

Inconclusive evidence and lack of agreement in outcomes for in-vitro orthodontic bond strength.

Steven Jefferies MS, DDS, PhD
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Overview

Systematic Review Conclusion

While laboratory orthodontic bond strength studies cannot be regarded as a substitute for in-vivo testing; variability of outcomes reported in these laboratory bond strength studies could be reduced with better standardization of test conditions, and thus provide a more reliable methodology for initial screening and selection of materials.

Critical Summary Assessment

Three specific experimental conditions (water storage, polymerization time, and testing strain-rate) significantly affected in-vitro strength testing, and should be examined carefully in assessing these reports. Overall, the strength of evidence is weak, the bias is high; hence, clinicians should be cautious in the interpretation and utilization of current laboratory bond strength data in clinical decision-making in this area of orthodontic treatment.

Conclusion:

Variability in testing parameters (water storage of the bonded specimens, photopolymerization time, and crosshead speed) appear to create a high degree of variability in laboratory results. This finding strongly suggests that in-vitro enamel bond strength testing, currently, provides limited guidance in the clinical orthodontic practice regarding selection of new materials and techniques for use with enamel-bonded brackets and appliances.

Source of Funding:

Not stated or indicated.

Commentary

Importance and Context:

Orthodontic adhesive bonding of brackets to teeth is a standard, common-place procedure in comprehensive orthodontic treatment using fixed appliances to control tooth movement in all dimensions. Due to the limited number of randomized controlled clinical studies evaluating the clinical performance of orthodontic adhesives, in-vitro bond strength testing of these adhesives assumes added significance in assessing potential clinical efficiency and effectiveness. Review of the literature and assessment of testing variables for this procedure is essential to establish test validity and reliability, as well as provide a basis for improving and standardizing test methods.

Strengths and Weaknesses of the Systematic Review:

This comprehensive, systematic review included a search of only two databases, and inclusion and exclusion criteria were not always clearly explained or defined. The authors did establish criteria for quality of studies evaluated. Interobserver agreement (Cohen kappa) for reporting the 27 experimental conditions of the included studies was 0.86. The authors did not analyze publication bias, but tests for heterogeneity among studies concluded that there was significant "clinical" heterogeneity. This systematic review did not state that a sensitivity analysis to determine robustness of the data was conducted. Exclusion of languages other than English may have eliminated potentially useful or important studies. Assuming that such efforts would have produced fruitful information, failure to perform hand searching for recent articles, to extend the search to include additional data bases, and to contact authors were limitations.

Strengths and Weaknesses of the Evidence:

As this systematic review included only in-vitro observational studies, with a lack of consistency in the data; the strength of evidence is weak, and the bias is high. The predominant use of shear bond strength testing on buccal enamel of pre-molars contributed to the strength of the data in the study literature. The lack of standardization or consistency in test methods for in-vitro orthodontic bond strength testing, revealed by this systematic review and meta-analysis,limited the strength of the evidence analyzed.

Implications for Dental Practice:

Bond strength of orthodontic adhesives must provide durability and reliability during the treatment phase to optimize treatment time and minimize the additional cost and burden of care if additional appointments are required for re-bonding. The adhesive bonding strength should not interfere with bracket debonding at the end of treatment, which would be an important future in-vitro study. Standardized of in-vitro test protocols for orthodontic adhesives could provide more consistent data to guide clinicians in evaluation and selection of adhesives. Hence, clinicians should be cautious in the interpretation and utilization of current laboratory bond strength data in clinical decision-making.